Apparatus and method for cutting holes

ABSTRACT

An annular hole cutter wherein each tooth is formed with a radially outer cutting edge and at least alternate teeth are formed with radially extending, circumferentially staggered inner and outer cutting edges. The bottom face of each tooth is formed with oppositely radially inclined inner and outer back-off faces which intersect in a downwardly extending crest which in turn intersects the radially outer cutting edge. The outer back-off faces of alternate teeth are vertically relieved relative to the outer back-off faces of the intermediate teeth and the inner back-off faces of the intermediate teeth are vertically relieved relative to the inner back-off faces of the alternate teeth a distance greater than the chip load at which the cutter is operated. In the preferred form, the radially inner portion only of the unrelieved inner back-off face is relieved to a greater extent than the relieved inner back-off faces.

This application is a continuation of Ser. No. 07-326,137 filed on Mar.20, 1989, now U.S. Pat. No. 4,952,102, which is a continuation of Ser.No. 07-178,829, filed Apr. 1, 1988, now U.S. Pat. No. 4,813,819, whichis a continuation of Ser. No. 06-909,398, filed Sep. 19, 1986, nowabandoned, which is a continuation of Ser. No. 06-787,039, filed Oct.15, 1985, now U.S. Pat. No. 4,632,610, which is a continuation of Ser.No. 06-522,181, filed Aug. 12, 1983, now abandoned, which is a CIP ofSer. No. 06-423,704, filed Sep. 27, 1982, now abandoned.

This invention relates to annular hole cutters.

Experience has shown that the life and the efficiency of a hole cutter;that is, the ease with which it can be fed through a metal workpiece,and the finish produced by an annular hole cutter are, to a very largeextent, dependent upon the ease with which the chips are cut and theease with which the chips being cut are enabled to flow away from thecutting edges and into and upwardly through the flutes around the outerperiphery of the cutter. When the chips formed by an annular hole cuttercannot move freely away from the cutting edges and/or the flutes becomepacked or clogged with chips, the torque and thrust required to feed thecutter increases, the cutter wears more rapidly and the finish of thehole being cut deteriorates.

Previous attempts to increase the efficiency of annular hole cuttershave met with some degree of success. For example, in my U.S. Pat. No.3,609,056 there is illustrated an annular cutter wherein each tooth isdesigned to cut a single chip. The successive teeth are divided intogroups of three and each tooth in each group is shaped to cut a chiphaving a width of about one-third the width of the tooth. In my U.S.Reissue Pat. No. 28,416 there is disclosed an annular hole cutterwherein each tooth is formed with a plurality of radially extending,circumferentially staggered cutting edges. The bottom face of each toothis formed with oppositely radially inclined back-off clearance faceswhich intersect in a downwardly extending crest which in turn intersectsthe radially outer cutting edge. Each cutting edge is designed to cut anindividual chip. While each tooth cuts a plurality of chips, theconfiguration of the cutter is such that the widest chip cut has a widthno greater than the depth of the flutes around the outer periphery ofthe cutter. In that particular cutter the web portion of the cutter sidewall is formed with a single inner cutting edge. More recently cuttershave been made which differ from those disclosed in Reissue U.S. Pat.No. 28,416 in that, in the more recent cutters, the web portion of thecutter is formed with two circumferentially staggered cutting edges,rather than a single cutting edge. While these more recent cuttersenable the use of a thicker web and a shallower flute, nevertheless theydo not always perform satisfactorily, especially when used in a highproduction application.

I have determined that the difficulty encountered in attempting toobtain a free, unimpeded chip flow outwardly through the flutes of anannular cutter results primarily from the fact that, as soon as a chipis cut it expands in all directions. Thus, immediately after being cut achip has a width greater than the width of the cutting edge by means ofwhich it was cut. In the case of the cutters having circumferentiallystaggered cutting edges on each tooth, if the width of the chips cut bythe inner cutting edges on each tooth is less than the depth of theflutes around the outer periphery of the cutter and if such chips arerelatively stiff, then at least theoretically they should not tend toclog the flutes. However, the free flow of these narrow chips upwardlythrough the flutes is actually impeded in many cases by the chips cut bythe outer cutting edges. In the cutters having circumferentiallystaggered cutting edges, the outer cutting edges terminate at theirradially inner ends against a circumferentially extending shoulder onthe cutter. Therefore, when the chip cut by such outer cutting edgeexpands, it tends to bind between this shoulder and the wall of the holebeing cut. This impedes movement of the chip upwardly away from thecutting edge; a condition which requires increased torque and muchgreater thrust and leads to more rapid tool wear and inferior surfacefinish. Under certain conditions in cutting of some materials cloggedflutes and broken blades frequently result.

The problem of binding of the chip cut by the outer cutting edge isobviously present in cutters of the type shown in Reissue U.S. Pat. No.28,416. In addition, where the inner cutting edge extends across thefull thickness of the web between successive teeth, flow of therelatively wide chip cut by this inner edge radially outwardly into theadjacent flute is frequently impeded.

The primary object of this invention is to provide a cutter that cutsefficiently and is designed to promote a free unimpeded flow of chipsthrough the flutes of the cutter from all cutting edges of the teeth.

Another object of this invention is to provide a cutter of the typepreviously described wherein the outer cutting edges are so designed asto cut a chip having a width substantially less than the width of theouter cutting edges and, thus, avoid the binding problem discussedabove.

A further object of this invention is to provide an annular cutter withstaggered cutting edges designed such that both the inner and outercutting edges cut chips which are of less width than the respectivecutting edges.

A more specific object of the present invention is to overcome theproblem of binding of chips produced by the outer cutting edges of afluted annular hole cutter having staggered inner and outer cuttingedges by vertically relieving the outer back-off faces of every othertooth and vertically relieving the inner back-off faces of theintermediate teeth so that the radially outer portion of the outercutting edge of one tooth cuts a heavy chip having a width substantiallyless than the width of the outer cutting edge and the radially innerportion of the outer cutting edge of the next successive tooth also cutsa heavy chip of approximately the same width, both of said chips beingsubstantially narrower than the depth of the flute.

In the preferred form, the width of the inner cutting edge correspondsto the web thickness and the radially inner portion of the unrelievedinner back-off faces is relieved to a greater extent than the relievedback-off faces.

Other objects, features and advantages of the present invention willbecome apparent from the following description and accompanyingdrawings, in which:

FIG. 1 is a perspective view of a cutter in accordance with the presentinvention;

FIG. 2 is a fragmentary perspective view of the cutter;

FIG. 3 is a fragmentary view of the cutter as viewed from the front faceof one of the cutter teeth;

FIG. 4 is a bottom plan view of the tooth shown in FIG. 3;

FIG. 5 is a fragmentary view of the tooth next successive to that shownin FIG. 3;

FIG. 6 is a bottom plan view of the tooth shown in FIG. 5;

FIG. 7 is a view showing the progression of the successive teeth of thecutter into a workpiece;

FIG. 8 is a perspective view of a modified cutter of the presentinvention;

FIGS. 9, 10, 11, 12 and 13 are views of the modified cutter whichcorrespond to FIGS. 2 thru 6, respectively;

FIG. 14 is a view showing the progression of two successive teeth of thecutter into a workpiece in FIGS. 8 thru 13; and

FIGS. 15 and 16 are fragmentary views of two successive teeth of afurther modified form of cutter.

The annular hole cutter of this invention is designed for forming holesin metal and is generally designated 10 in FIG. 1. The cutter includes abody 12 and a shank 14. Cutter body 12 is of inverted cup shape having aside wall 16 the length of which is greater than the thickness of theworkpiece in which the hole is to be cut. The lower end of side wall 16is formed around its periphery with a plurality of circumferentiallyspaced cutting teeth. In the embodiment illustrated the cutting teethare divided into two groups, those of the first group being designated18 and those of the second group being designated 20. The teeth 18,20are alternately arranged so that one tooth 20 is disposedcircumferentially between successive teeth 18. A spiral flute 22 extendsupwardly around the outer periphery of the cutter adjacent each tooth.The successive flutes 22 are separated by a land 24 at the outerperiphery of the cutter. The leading edge of each land 24 is formed witha narrow margin 25. The portions of the annular side wall 16 of thecutter between successive teeth 18,20 comprise webs 26. The radiallyouter face 28 of each web 26 defines the radially inner wall of eachflute 22. The depth of flute 22 is approximately equal to or can beslightly greater or less than the thickness of web 26. Each fluteincludes a circumferentially leading side wall 30 and acircumferentially trailing side wall 32.

In the cutter illustrated in the drawings each tooth 18,20 is formedwith three cutting edges 34,36,38. Cutting edge 38 has two portions38a,38b as hereinafter explained. Cutting edge 34 is spaced forwardly inthe direction of rotation from cutting edge 36 and cutting edge 36 isspaced forwardly in the direction of rotation from cutting edge 38.Cutting edge 34 is located at the lower end of the trailing face 40 ofan inner gullet 42 formed in web 26. The upper end of gullet 42 inclinesradially outwardly in an upward direction as at 44. Cutting edge 36 islocated at the lower end of the trailing face 46 of a secondary gullet48 which is also formed in web 26 directly adjacent inner gullet 42. Theupper end of secondary gullet 48 is curved upwardly in a radiallyoutward direction as at 50 above inner gullet 42. Cutting edges 34,36are separated by a circumferentially extending shoulder 51 at the lowerend of the radially inner face 52 of gullet 48. Cutting edge 38 islocated at the lower end of the trailing face 32 of flute 22 and isspaced rearwardly from cutting edge 36 by a shoulder 54 at the lower endof flute 22.

The bottom face of each tooth is formed with two back-off clearancefaces 56,58. In the operative condition of the cutter (FIG. 1), radiallyinner back-off face 56 inclines axially upwardly and radially inwardlywhile the radially outer back-off face 58 inclines axially upwardly andradially outwardly. In addition, each of these back-off faces inclinesupwardly from its respective cutting edges in a circumferentialdirection to a slight extent, say 8° to 10°, to provide the necessaryclearance for the cutting edges as the tool is rotated. The two back-offfaces 56,58 intersect in a downwardly extending crest 60 which in turnintersects the radially outermost cutting edge 38 so as to divide itinto a radially outer edge portion 38a and a radially inner edge portion38b. The radial inclination of back-off face 58 is in the range ofbetween about 5° to 35° to the horizontal and is preferably about 10°.The inner back-off face 56 inclines radially to the horizontal at anangle of between -3° to +25°, and preferably about 15°. As a result ofthe inclination of back-off faces 56,58 in both a radial and acircumferential direction, cutting edges 34,36,38 are not only staggeredcircumferentially as shown in FIGS. 4 and 6, but are also staggeredvertically when viewed from the front face of the tooth as shown inFIGS. 3 and 5.

With the cutter thus far described the chips cut by the cutting edges34,36 would be narrower than the depth of flutes 22 and would thereforebe readily accommodated by the flutes. However, when the cutting edge 38cuts a chip across its full width, as soon as this chip is cut, itexpands and tends to bind between shoulder 54 and the wall of the holebeing cut. The purpose of the present invention is to avoid this bindingeffect by having each outer cutting edge 38 cut a chip having a widthless than the width of edge 38.

It will be observed that the crest 60 on the teeth 18 is disposedradially inwardly of the crest 60 on the teeth 20. The radiallystaggered crests 60 on the successive teeth of the cutter result fromthe fact that on each tooth 18 the back-off face 58 is verticallyrelieved throughout its radial extent upwardly relative to the back-offface 58 of each tooth 20. This in itself would result in crest 60 ofeach tooth 18 being disposed radially inwardly relative to crest 60 ofeach tooth 20. In accordance with the invention, the back-off face 56 ofeach tooth 20 is likewise relieved throughout its radial extent upwardlyrelative to the back-off face 56 of each tooth 18. The relieving of theback-off faces 56 of the teeth 20 displaces the crests 60 radiallyoutwardly from the crests 60 on teeth 18 an additional extent.

The degree to which these back-off faces are relieved vertically is notcritical, but, in any event, must be greater than the desiredtheoretical chip load on each tooth. For example, if a six-tooth cutteris advanced 0.012" per revolution, the theoretical chip load on eachtooth is 0.002". Thus, if the theoretical chip load on each tooth is0.002", then back-off faces 56,58 should be vertically relieved asdescribed above a distance greater than 0.002". As a practical matter,assuming that a 0.002" chip load is a normal minimum chip load at whicha tool may be operated and that a chip load of about 0.005" is a normalmaximum chip load at which an annular cutter of this type is operated,then the vertical relief on the back-off faces 56,58 should be in therange of between 0.003 to 0.012". However, with large heavy cutters thefeed rate may be such as to produce a chip load substantially in excessof 0.005"; then the relief may be as high as 0.020". As a practicalmatter, it is preferred to relieve these surfaces in the amount of about0.007 to 0.010:, and preferably about 0.009". It should be appreciatedthat the maximum extent of relief is related to the radial inclinationangles of the back-off faces and the width of the outer cutting edge sothat, when relieved, crest 60 still intersects the outer cutting edge38, not the intermediate cutting edge 36.

It is highly desirable to relieve the inner and outer back-off facessuch that the crests of successive teeth are spaced approximatelyradially equally from the radial center line of the flute. When thecrests are so located the outer cutting edges of successive teeth willcut chips of approximately equal width, each being only sightly widerthan one-half the flute depth. This results in all chips having maximumclearance within the flutes 22.

The cutting action produced by the tool as heretofore described is bestillustrated in the progressive views of FIG. 7. These views depict anannular cutter of the type described having six teeth. The teethdesignated 1, 3 and 5 (indicated at the left of FIG. 7) correspond tothe teeth 18 on which the back-off face 58 is vertically relieved andthe teeth designated 2, 4 and 6 in FIG. 7 correspond to the teeth 20 onwhich the radially inner back-off face 56 is vertically relieved. Thesuccessive views of FIG. 7 progressing in a downward direction depictthe action of the successive teeth of the cutter for successiverotational increments equal to the pitch between successive teeth.

In view a of FIG. 7 the cutter is illustrated at a position wherein thecutting edge 36 has just begun to penetrate the top surface of theworkpiece and thus cut a narrow chip 62 from the top face of theworkpiece. At this position the upwardly relieved cutting edge 38 oftooth #1 has not yet engaged the workpiece and the lowest point ofcutting edge 34 is about to engage the workpiece. When the cutter hasrotated one tooth pitch and advanced axially from the position shown inview a of FIG. 7, the cutting edge 38 of tooth #2 cuts into theworkpiece to produce a chip 64. The cutting edges 34,36 on tooth #2 arevertically relieved a distance greater than the theoretical chip loadproduced by the axial feed rate and, thus, the cutting edge 36 isactually spaced above the groove previously formed by the correspondingedge 36 of tooth #1.

Upon the next increment of rotation and axial advance of the cutter(view c) the chip 62 produced by the cutting edge 36 of tooth #3 will berelatively thick since this cutting edge is not vertically relieved andcutting edge 34 of tooth #3 will cut the chip designated 66. Theradially inner portion of cutting edge 38 on tooth #3 will initiate acut and produce a chip 68. When the tool rotates through anotherincrement (view d) the radially outer portion of cutting edge 38 cuts awider and deeper groove than previously cut by edge 38 of tooth #2 sothat chip 64 is wider and thicker than the chip produced by the innerportion of cutting edge 38 of the previous tooth. Since the edges 34,36of tooth #4 are vertically relieved a distance greater than the chipload, they are spaced above the bottoms of the groove formed by thecorresponding cutting edges of tooth #3. View e illustrates the cuttingaction of tooth #5 after an additional increment of rotation and feed.Cutting edges 34,36 are now cutting a full width chip 62,66, but onlythe radially inner portion of cutting edge 38 is effective so that thechip 68 cut thereby is wider than the chip cut by the inner portion ofcutting edge 38 of tooth #3.

Although the chips 62,66 correspond in width with the cutting edges36,34, respectively, and even though these chips expand somewhatimmediately after being formed, they will not tend to bind within thecutter if they are relatively narrow because, as soon as chip 66 isformed, it is directed radially outwardly into the adjacent flute 22 bythe upper face 44 of gullet 42. Likewise, as soon as chip 62 is formed,it is directed radially outwardly into the adjacent flute 22 by theupper surface 50 of the secondary gullet 46. Thus, the narrow chipsformed by the cutting edges 34,36 are directed into the adjacent flute22 immediately after being formed and, since the radial depth of flute22 is substantially greater than the width of chips 62,66, they normallyflow freely up the flute in an unimpeded manner.

From the showing in views e through j of FIG. 7 it will be observedthat, after all of the cutting edges have penetrated into the workpiece,each of the cutting edges 38a and 38b will produce a chip of less widththan the total width of cutting edge 38. Thus, the radially outerportion of edge 38 on each alternate tooth cuts a chip 64 and theradially inner portion of each cutting edge on the intermediate teethcuts a chip 68. Consequently, since each of the chips 64,68 are narrowerthan the radial depth of flute 22, these chips move freely through theflutes.

Since the back-off faces 56,58 are alternately relieved vertically asdescribed to an extent greater than the theoretical chip load, it willbe appreciated that, after all the teeth have penetrated into the work,all of the chips are relatively thick and have an actual maximumthickness greater than the theoretical chip load. When chips arerelatively thick, they tend to remain generally straight rather thantightly curled; therefore, they do not tend to intertwine with otherchips and, thus, flow more readily upwardly through the flutes of thecutter. In addition, since all of the back-off faces 58 are inclined tothe horizontal at a relatively low angle, preferably about 10°, thechips cut primarily by edge portion 38a are directed generally straightup the flute rather than radially inwardly against the radially innerface of the flute. This enhances the unimpeded free flow of all of thechips formed by the cutting edges upwardly through the flutes.

As pointed out previously, when the flow of chips away from the cuttingedges and upwardly through the flutes is unimpeded, the torque andthrust required to drive the cutter are radically reduced. Likewise, thecutting edges are dulled at a much less rapid rate and the life of thecutter is prolonged. In addition, since the cutting edges remain sharpand since the chips do not bind against the wall of the hole being cut,the surface finish obtained is substantially superior to that obtainedwith prior art cutters.

In accordance with the present invention, the cutting edges 34,36 ofonly alternate teeth provide a cutting action. Since the cutting edges34,36 of the teeth 20 (namely, the teeth numbered 2, 4 and 6 in theembodiment illustrated in FIGS. thru 7) do not perform any cutting, thecutting edges 34,36 on these teeth may be omitted entirely. This can beeasily accomplished by grinding each tooth 20 completely along the widththereof as indicated by the broken radial line 70 in FIGS. 2 and 4. Inthis event only the teeth 18 will be provided with inner cutting edges34,36. When the teeth 20 are formed with only a single outer cuttingedge 38, the circumferential extent of each tooth 20 is relatively shortand, since each tooth 20 will cut only a single narrow chip, theadjacent flute 22 can be substantially narrower circumferentially thanthe flutes adjacent the teeth 18 which must accommodate three narrowchips. Thus, when teeth 20 are formed with only a single cutting edge, agreater number of teeth can be formed on a cutter of a predetermineddiameter. The greater number of teeth results not only in a strongercutter, but also in more rapid cutting at the same surface speed. Inaddition, since only a portion of the cutting edges on each tooth isactually cutting, the remaining portions are readily inundated withcoolant flowing downwardly through the passageway in the shank of thecutter so that the heat generated can be rapidly dissipated.

The cutter illustrated in FIGS. 8 thru 14 is generally of the type shownin U.S. Reissue Pat. No. 28,416. It differs from the cutter previouslydescribed primarily in that each tooth is formed with only two cuttingedges, rather than three, the inner cutting edge 35 extending across thefull thickness of the web 26. For reasons hereinafter explained, eventhough the inner cutting edge 35 corresponds in width with the thicknessof web 26, the web 26 can have a thickness equal to approximatelyone-half or slightly greater than the wall thickness of the cutter.Since the inner cutting edge 35 extends across the full width of thecutter, it is only necessary to provide a single gullet 42 betweensuccessive teeth.

As in the previous embodiment described, the outer back-off faces 58 ofteeth 18 are vertically relieved and the inner back-off faces 56 ofteeth 20 are similarly relieved. Thus the crests 60 of the successiveteeth are staggered radially in the same manner as the embodimentpreviously described. However, in the embodiment illustrated in FIGS. 8thru 14 where the inner cutting edge 35 extends across the fullthickness of web 26, the inner back-off faces 56 of the teeth 18 arerelieved as shown in FIGS. 9, 12 and 13. These back-off faces arerelieved upwardly through only a portion of their width; namely, theradially innermost portion. This divides the inner cutting edges 35 ofteeth 18 into a radially inner portion 35a and a radially outer portion35b. As shown in FIGS. 9 and 13, the back-off faces 56 of teeth 18 arerelieved in this manner throughout their entire circumferential extentso that the back-off faces 56 are divided into two portions 56a and 56b,the line of intersection therebetween being designated 61.

At the cutting edge 35 the line of intersection 61 is preferably spacedradially inwardly from shoulder 54 a distance of between one-quarter andone-half the thickness of web 26. As explained hereinafter, thisproduces chips of desired size by the inner cutting edges. Since theinner back-off faces 56 of teeth 20 are relieved, in order to obtain thedesired cutting action it is essential that the surfaces 56b of theteeth 18 be relieved to a greater extent, preferably between two andthree times the relief of back-off faces 56 of teeth 20. For example, ifthe back-off faces 56 of teeth 20 are relieved about 0.010", then theextent of relief of the back-off faces 56b of teeth 18 should be about0.020 to 0.030" at the inner periphery of the cutter.

The cutting action produced by the tool shown in FIGS. 8 thru 13 is bestillustrated in the progressive views of FIG. 14. Since the back-offfaces 56,58 of the successive teeth are relieved in the same manner asin the previous embodiment described, it follows that the outer cuttingedges 38 of the successive teeth will produce the chips designated 64and 68 in FIG. 14 which are similar to the corresponding chipsillustrated in FIG. 7. However, the inner cutting edges of thesuccessive teeth will each cut a chip having a width less than the widthof cutting edge 35. Since the back-off faces 56b of each tooth 18 arerelieved as shown in FIGS. 12 and 13, it then follows that the radiallyouter portion of the cutting edge 35 on each tooth 18 will cut a chip,designated 63b in FIG. 14, and the radially innermost portion of thecutting edges 35 on each tooth 20 will produce a chip 63a. The widths ofthe chips 63a and 63b will depend upon the radial location of the lineof intersection 61. Since the radially innermost chip 63a has to travelradially a greater distance to reach a flute 22 of the cutter, it ispreferred that the chips 63a are dimensioned in width less than thechips 63b. Thus, as shown in FIG. 14 wherein the line of intersection 61is spaced from the shoulder 54 a distance about one-third the thicknessof web 26, the chip 63a is substantially narrower than the chip 63b.

A further modification of the invention is illustrated in FIGS. 15 and16. The cutter illustrated in this embodiment is generally the same asthat illustrated in FIGS. 8 thru 14 in that the cutter has a singlecutting edge (designated 37) on the web portion of the cutter, but couldhave two cutting edges as illustrated in FIGS. 1 thru 7. The back-offfaces of the successive teeth are alternately relieved as in theprevious embodiments described, but in a slightly different manner.Thus, the teeth as originally formed have inner back-off faces 56 andouter back-off faces 58 which intersect in a downwardly extending crest63. On each tooth 18 (FIG. 16) the outer back-off face 58 is verticallyrelieved from the crest 63 to the outer periphery of the cutter, asindicated at 58c. The extent of relief of the back-off face 58c at theouter periphery of the cutter is in the range previously referred to;namely, between 0.003 and 0.020" depending upon the intended chip load,and preferably in the range of about 0.007 and 0.010". In like manner,the inner back-off faces 56 of teeth 20 (FIG. 15) are verticallyrelieved upwardly the desired extent from crest 63 in a radially inwarddirection, as indicated at 56d. When the successive teeth are relievedin this manner the crests 63 of all teeth remain in the same axial andradial position. This is desirable in small diameter cutters having afew number of teeth. For example, when the cutter has only four teeth,all four crests 63 will engage the workpiece and initiate and cut at thesame time and, thus, produce less chatter and greater accuracy than ifonly two of the crests initially engaged the workpiece.

FIG. 16 also illustrates a modified method of relieving the radiallyinnermost portion of the inner cutting edge 37. In this modification theinner cutting edge of each tooth 18 is divided into radially inner andportions 37a and 37b by grinding a vertical shoulder on the innerback-off face 56, as indicated at 37c. As in the embodiment illustratedin FIGS. 8 thru 14, the vertical relief imparted to the cutting edgeportion 37a should be greater, preferably between two and three timesthe relief provided at the inner edge 37 of the teeth 20. The locationof the shoulder 37c in a radial direction is determined by the samefactors which govern the location of the line of intersection 61 of thecutter illustrated in FIGS. 12 and 13; namely, the desired relativesizes of the chips produced by the successive inner cutting edges.

I claim:
 1. A method for cutting holes in a workpiece with an annularhole cutter which has a plurality of cutting teeth spacedcircumferentially around one end of the cutter, the cutting teeth aredivided into a first set of teeth and a second set of teeth with each ofthe teeth having at least one radially extending cutting edge and withthe teeth in the first set having the same configuration and the teethin the second set having the same configuration but different than theconfiguration of the teeth in the first set;a plurality of chip passagesextending along the side of the cutter away from the teeth with each ofthe cutting edges having a chip passage adjacent thereto; the methodincluding the steps of:(1) rotating the annular hole cutter and engagingthe workpiece with the annular hole cutter; (2) cutting into theworkpiece with the annular cutter with at least one of the cutting edgeson each of the teeth cutting a chip from the workpiece with each chiphaving a width measured generally radially which is less than the radialdepth of the adjacent chip passage; (3) continuing step (2) until theannular cutter cuts to the desired depth.
 2. The method of claim 1,wherein the annular cutter cuts a circumferential path with each of theteeth of the firsts set of teeth having at least one cutting edgecutting a chip along the outer most portion of the circumferential pathand each of the teeth of the second set of teeth having at least onecutting edge cutting a chip from another portion of the circumferentialpath.
 3. The method of claim 1, wherein the annular cutter cuts acircumferential path with each of the teeth of the first set of teethcutting two chips from the middle portion of the path and each of theteeth of second set of teeth cutting two chips from the outer most andinner most portions of the path.
 4. An annular hole cutter having agenerally cylindrically side surface and a plurality of generallyequally spaced cutter teeth at one end divided into first and secondsets with the teeth of the first set having substantially the sameconfiguration and the teeth of the second set having substantially thesame configuration but different than that of the first set and witheach tooth of both sets having at least one outer cutting edge and anadjacent cutting edge, these cutting edges being circumferentially speeddefining a shoulder between the outer and adjacent cutting edges;aplurality of generally channel-shaped first chip passages extending fromadjacent cutter teeth upwardly around the outer periphery of the sidesurface; a plurality of second chip passages directly adjacent thecutter teeth which communicate with the first chip passages, the secondchip passages having a radial depth defined by the maximum radialdistance between the shoulder and outer wall of the hole being formed bythe cutter; the cutting edges being configured to cut a plurality ofchips from a workpiece with each chip having a width as measuredgenerally radially which is less than the radial depth of the first orsecond chip passages.
 5. The annular hole cutter of claim 4, wherein theplurality of cutting teeth form a group of alternate cutting teeth and agroup of intermediate cutting teeth interposed between said alternatecutting teeth, said first set of teeth having one cutting edge cutting asingle chip and said second group of teeth having more than one cuttingedge cutting more than one chip.
 6. The annular hole cutter of claim 4,wherein each of said teeth has more than one cutting edge with eachcutting edge cutting a single chip such that each tooth cuts more thanone chip.
 7. The annular hole cutter of claim 4, wherein the pluralityof cutting teeth form a group of alternate cutting teeth and a group ofintermediate cutting teeth interposed between the alternate cuttingteeth, one group has radially inner and outer back-off faces extendingcircumferentially rearwardly and inclined upwardly from said cuttingedge with each outer back-off face inclined downwardly in a radiallyinward direction and the outer and inner back-off faces intersecting ina generally circumferentially extending crest which, at its forwardextent intersects the cutting edge;the other group of teeth has at leastone back-off face extending circumferentially rearwardly and inclinedupwardly from the cutting edge.
 8. The annular hole cutter of claim 5,wherein the teeth cut chips from the workpiece to form a kerf having aspecific radial width with neither set of teeth being configured to cutthe full width of the kerf.
 9. The annular hole cutter of claim 8,wherein the alternate teeth cut at least one chip from the kerf and theintermediate teeth cut at least two chips from the kerf.
 10. The annularhole cutter of claim 8, wherein the alternate teeth cut at least onechip from the middle portion of the path and the intermediate teeth cuttwo chips, one chip from the outer most portion of the kerf and one chipfrom the inner most portion of the kerf.
 11. The annular hole cutter ofclaim 8, wherein the alternate teeth cut two chips from the middleportion of the kerf and the intermediate teeth cut two chips from theouter most and inner most portion of the kerf.